Gravity cannon only appears in the Elona+ version of Elona. It is a stronger, 3rd tier version of the Yerles self-propelled gun; it looks like one except tinted purple. It is even stronger than a security system. It has access to the Gravity Sphere special action which it will repeatedly use if you are too far away from its effective gun range, doing dangerous amounts of damage. Low life pets such as bells and casters can be taken out in one hit by this. It can spawn in groups making them extremely dangerous at range.